DnaA proteins of Escherichia coli and Bacillus subtilis: coordinate actions with single-stranded DNA binding protein and interspecies inhibition during open complex formation at the replication origins

DnaA-mediated unwinding of the AT-rich region in the replication origins of Escherichia coli and Bacillus subtilis was analysed in vitro with and with out single-stranded DNA-binding protein (SSB). In the presence of SSB, the unwound region was larger by a defined number of base pairs. Although the o verall structure of the origins is very different, the size and structure o f the unwound region were similar. The unwinding reaction at oriC of one or ganism was inhibited by DnaA protein of the other bacterium. Similarly, hyb rid DnaA proteins with swapped DNA-binding domains were inactive and inhibi tory to 'open complex formation at both origins. We suggest that the inhibi tion is due to inactive mixed complexes. (C) 1999 Elsevier Science B.V. All rights reserved.